The rates of oxidation of the alpha and beta subunits of hemoglobin by ferricyanide were found to be about equal. Reaction of hemoglobin with hydroxylamine between pH 7 and 9 produces two unidentified low-spin triplets in the electron spin resonance spectrum. Although these triplets do not correspond in position to those produced by reaction of several simple amines with ferric hemoglobin, one does correspond in position to a triplet produced by reaction of heme with a thiol and imidazole, suggesting that the ferric ion position ordinarily occupied by a water molecule or hydroxyl in methemoglobin is replaced by a cysteine sulf-hydryl when hydroxylamine reacts with hemoglobin. After venous injection of about 15 mg pentavalent antimony per liter, no trivalent antimony above the limits of polarographic detection (approximately 1 mg per liter) could be found, suggesting that conversion to the more toxic trivalent ion does not occur during the killing of the leishmaniasis trypanosome.